The following U.S. patents illustrate the best art known to the inventor at the time of the filing of this application.
U.S. Pat. No. 1,755,614 to Seil; Apr. 22, 1930 PA0 U.S. Pat. No. 2,684,330 to French; Jul. 20, 1954 PA0 U.S. Pat. No. 2,686,138 to Klein et al; Aug. 10, 1954 PA0 U.S. Pat. No. 2,815,943 to Lamb; Dec. 10, 1957 PA0 U.S. Pat. No. 2,826,209 to Klein et al; Mar. 11, 1958 PA0 U.S. Pat. No. 3,150,007 to Kovachy; Sep. 22, 1964 PA0 U.S. Pat. No. 3,880,965 to Dudis et al; Apr. 29, 1975 PA0 U.S. Pat. No. 4,238,244 to Banks; Dec. 9, 1980 PA0 U.S. Pat. No. 4,382,867 to Schmit et al; May 10, 1983 PA0 U.S. Pat. No. 4,419,141 to Kunkel; Dec. 6, 1983